This invention relates to a communication apparatus for sending and receiving data between a LAN (Local Area Network) and a network such as a SONET (synchronous optical network) network or a SDH (synchronous digital hierarchy) network, and to a method for setting the line capacity thereof.
SONET and SDH are known as typical synchronous communication systems. These are standard frame formats for effective transfer of various kinds of information with speeds varying from low speed to high speed. These have been standardized by ITU-T (International Telecommunication Union —Telecommunication Standardization Sector) and are now used worldwide mainly in backbone networks. SONET and SDH are not “synchronous communication systems” in the strict sense, since they generate misalignment of 1 byte per frame at the maximum. However, these systems will be regarded as “synchronous” in the description herein including the case where such misalignment occurs. Further, since SDH and SONET are essentially the same in their characteristics such as the frame structures and the multiplexing schemes, the following description will be focused on SONET.
Conventionally, a technique for interconnecting LANs via this SONET is known. This technique is referred to as Packet Over SONET and enables connection between IP (Internet Protocol) networks constituting LANs and a SONET network. Such connection is made by communication apparatus connected to both networks.
FIGS. 12 and 13 are schematic block diagrams of conventional communication apparatus for connecting IP networks and one or more SONET networks. FIG. 12 shows a configuration of a communication apparatus having one LAN interface, and FIG. 13 shows a configuration of a communication apparatus having a plurality of LAN interfaces.
These communication apparatus have one or more LAN interfaces as low speed interfaces connected to the IP networks and one or more SONET interfaces as high speed interfaces to which one or more SONET networks are connected. For example, in these communication apparatus, data (packets) sent from a LAN is processed within one of the LAN interfaces in a closed manner as long as the LAN interface can process the data. If the data cannot be processed within the LAN interfaces, it is sent to one of the SONET interfaces. The SONET interface converts the packets sent from the LAN interface into SONET frames and sends them to the SONET network.
Here, the communication apparatus shown in FIG. 12 has only one SONET interface for the LAN interface, and therefore it will send all packets to the SONET interface if it cannot route packets only by the LAN interface. That is, packets that cannot be routed by the LAN interface are all sent to the SONET interface, and an administrator of the apparatus has no way to change this configuration. While this method imposes little burden of operation and management for connecting the LAN interface and the SONET interface, it involves a problem that effectiveness of network use decreases unless SONET is appropriately set. When IP packets are converted into SONET frames, various formats according to the SONET standards are used, such as STS1, STS3C, and STS12C. For example, the amount of IP packets to be input to the communication apparatus is estimated to determine the capacity of SONET frames into which IP packets are to be converted. However, this correspondence needs to be preset and cannot be changed by the communication apparatus itself. Therefore, without appropriate setting of the capacity of SONET frames, IP packets that are input from the LAN cannot be efficiently sent to the SONET network; discarded IP packets increases and empty portions appear in SONET frames.
As to the communication apparatus shown in FIG. 13, it has a plurality of SONET interfaces for a plurality of LAN interfaces, and therefore it sends packets that cannot be routed by the LAN interfaces to an appropriate SONET interface. Here, the LAN interfaces and the SONET interfaces perform routing based on information available for an administrator of the apparatus in advance. Thus, appropriate packets are sent to an appropriate SONET interface from a LAN interfaces. With this method, selecting an appropriate SONET interface enables efficient use of the network if the network is stably operated, but the network configuration cannot be changed once it has been set. For example, it is difficult to make changes such as changing a data line into a line for graphic data or adding another data line. Such changes may be addressed by setting SONET frames in consideration of the maximum size of packets to be sent and received, and reserving redundant transmission capacity. However, generally it is rare that packets having a fixed volume are constantly sent and received, but the actual transmission volume of packets sent and received dynamically changes depending on the kinds and contents of data. This poses problems that empty portions appear in SONET frames and the efficiency of network use decreases.